This application relates to disc drives, and particularly to tuning the track density of the data storage medium of a data storage device to obtain minimal error rates.
Magnetic disc drives are commonly designed with a constant track density across the radius of the disc for both data and servo tracks. The track density is most often expressed as the number of tracks per inch (TPI). For any given family of drives, there will be a fixed number of data and servo tracks. The number of tracks per inch is primarily governed by the head specifications. The head specifications include a definition of off-track capability, which defines the ability of the read head to accurately read data when the head is not exactly centered on the data. If a head fails to meet the required off-track capability, the head fails qualification tests and is not used in the disc drive. Thus, each of the heads of the disc drive must meet the requirements of off-track capabilities.
Ordinarily, the off-track capabilities are inversely related to the head""s ability to read data at various track densities. A head with superior off-track capabilities at a required track density may have lower, but still adequate, off-track capability at a higher track density. Similarly, a head with inadequate off-track capabilities at a required track density may exhibit adequate off-track capabilities at a lower track density.
Current designs utilize a fixed data TPI scheme in which all of the data storage surfaces in the drive has the same track density so that every head of the drive is arranged to read and write at the same fixed TPI. If a multi-head drive has one head with inadequate off-track capabilities at the required track density, the drive will fail qualification tests even if the other heads have superior off-track capabilities at the same density. When a drive has one head that fails to meet design requirements, that drive must either be re-worked to replace the head, or reconfigured to a model having a lower storage capacity. There exists a need to compensate for the nominally inadequate heads in disc drives to meet performance requirements without replacing the head or reconfiguring the drive to one of lower capacity. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.
The present invention is directed to the selection of the track density for the data storage surfaces of a storage device such that a nominally inadequate head can be used in combination with a storage surface at a track density that is lower than required, while another head/surface combination operates at a track density that is higher than required and the drive specifications are met.
In one embodiment, data track densities on each of a plurality of storage surfaces of a data storage apparatus are defined. A minimum head quality rating is established for the data storage apparatus, and a head quality rating is identified for each of the heads for each of a plurality of track densities. A track density is selected for each head based on the minimum head quality rating and the identified head quality ratings. The selected track density is established for the storage surface associated with each respective head.
In some embodiments, the head quality rating is identified from an off-track capability for each head for each of a plurality of track densities. An error rate is identified for each head at each of the plurality of track densities. The head quality rating for each track density for each head is identified from the off-track capability and the corresponding error rate.
In some embodiments, the track density is selected by selecting a candidate track density for each head as that track density that matches the track density corresponding to the minimum head, quality rating. The average of the candidate track densities is compared to the nominal track density. The candidate track density is selected for each storage surface only if the average of the candidate track densities is at least as great as the nominal track density.
In another embodiment a data storage device includes a plurality of head/surface combinations each including a storage surface containing adjacent data storage tracks and a head arranged to transfer information with the data storage tracks. Means establishes different data track densities on at least two storage surfaces. In particular, the means establishing the data track density comprises an arrangement of the data storage tracks at densities defined by an off-track capability of the confronting head.
Other features and benefits that characterize the present invention will be apparent upon reading the following detailed description and review of the associated drawings.